1. Field of the Invention
The present invention relates to a liquid ejection head and an image forming apparatus, and more particularly, to a liquid ejection head and image forming apparatus whereby the bonding characteristics and reliability of a diaphragm and piezoelectric bodies are improved, and ejection force is increased.
2. Description of the Related Art
Conventionally, as an image forming apparatus, an inkjet printer (inkjet recording apparatus) is known, which comprises an inkjet head (liquid ejection head) having an arrangement of a plurality of nozzles (ejection ports) and which records images on a recording medium by ejecting ink from the nozzles toward the recording medium while causing the inkjet head and the recording medium to move relatively to each other.
In an inkjet printer of this kind, ink is supplied to pressure chambers from an ink tank, via an ink supply channel, and by driving piezoelectric elements by supplying electrical signals corresponding to the image data to the piezoelectric elements, the diaphragms constituting a portion of each pressure chamber are caused to deform, thereby reducing the volume of the pressure chamber and causing the ink inside the pressure chamber to be ejected from a nozzle in the form of a droplet.
In an inkjet recording printer, one image is formed on a recording medium by a combination of dots formed on the recording medium by ink ejected from the nozzles. In recent years, it has become desirable to form images of high quality on a par with photographic prints, in inkjet printers. It has been thought that high image quality can be achieved by reducing the size of the ink droplets ejected from the nozzles by reducing the diameter of the nozzles, while also increasing the number of pixels per image by arranging the nozzles at high density.
On the other hand, as a method of manufacturing an inkjet head, there is a method in which piezoelectric elements (piezoelectric bodies) and a diaphragm are manufactured separately and are then bonded together. In this case, with increase in nozzle density, the density and level of integration of the piezoelectric bodies formed on the pressure chambers corresponding to the nozzles have also increased, and it has been sought to achieve high accuracy of positioning when bonding piezoelectric elements with a diaphragm in this way.
As a method for achieving high positional accuracy when bonding piezoelectric elements with a diaphragm in this way, it has been proposed that recess and projection shapes be formed in either one or both of the piezoelectric elements and the diaphragm, in such a manner that reliable positional alignment can be achieved by mutually engaging the recesses and projections.
For example, a method is known in which a recess shape is provided in the bonding surface of either a laminated piezoelectric element or a pressure transmitting member for transmitting the deformation of the laminated piezoelectric element to a diaphragm, and a projecting shape is provided in the bonding surface of the other thereof, and by assembling the element and member in such a manner that these shapes are mutually engaging, variation in positional accuracy is eliminated and reliability is improved. Furthermore, by forming the bonding sections with projecting and recess shapes, only the active section of the laminated piezoelectric element transmits vibration, and therefore, it is possible to avoid decline in the displacement due to the bonding surface failing to perform sufficient movement in cases where both the active section and the inactive section of the laminated piezoelectric element make contact with the diaphragm. Consequently, displacement efficiency is improved (see, for example, Japanese Patent Application Publication No. 6-188472).
Furthermore, Japanese Patent Application Publication No. 6-188472 describes a method in which, even if there is difference between the heights of a base substrate and a pressure transmitting member, the difference in height is absorbed by an adhesive deposited on the bonding surfaces of a laminated piezoelectric element and the pressure transmitting member, and therefore the volume of the pressure chambers can be made uniform, even if there are height variations between respective members. Since the laminated piezoelectric element and the pressure transmitting member are bonded by means of an adhesive, the deformation of the piezoelectric element is transmitted to the pressure chamber, and a uniform ejection efficiency can be maintained.
Furthermore, it is also known that the reliability of a diaphragm can be improved if, for instance, a first layer comprising a thin film made from a metallic material capable of deforming due to displacement of a laminated piezoelectric element, and a second layer comprising a thick film made of metallic material are layered in a unified manner onto a diaphragm plate, the second layer only on the diaphragm plate then being etched selectively to form island-shaped projections corresponding to the laminated piezoelectric elements and diaphragm sections surrounding same, and the island-shaped projections being bonded with the drive sections (active sections) of the laminated piezoelectric elements (see, for example, Japanese Patent Application Publication No. 9-290506).
Furthermore, it is also known that a thin film diaphragm plate free of pinhole defects can be formed by, for example, etching a diaphragm plate to achieve a thin film of 10 μm or less, thereby forming diaphragm sections, and also forming island-shaped projections corresponding to the active sections of laminated piezoelectric elements, and then pressure bonding the laminated piezoelectric elements with the island-shaped projections on the diaphragm plate (see, for example, Japanese Patent Application Publication No. 2001-10050).
Moreover, for example, it is also known that, by forming island-shaped projections on a diaphragm plate, forming recess sections in the bonding surface of piezoelectric elements which are to be bonded with the diaphragm plate, aligning the positions of the island-shaped projections and the recess sections on the piezoelectric elements, and then bonding same by means of a film type adhesive, such as an epoxy thermosetting resin, which can be applied to a high degree of accuracy, then the piezoelectric elements and the diaphragm plate can be aligned in position with high accuracy, the positioning accuracy of the piezoelectric elements and the pressure chambers can be raised, and therefore it becomes possible to adapt to increased density of the nozzle pitch (see, for example, Japanese Patent Application Publication No. 2000-334949).
However, all of the above-described related arts involve forming projecting shapes or recess shapes in both the diaphragm and the piezoelectric elements, and the manufacture of these shapes brings problems of the following kinds.
For example, in Japanese Patent Application Publication Nos. 9-290506 and 2001-10050, etching is used in order to create projecting shapes in a diaphragm plate, and therefore, this processing step is complicated and production efficiency is poor. In Japanese Patent Application Publication No. 2000-334949, a wire saw is used as a device for forming recess shapes in the piezoelectric elements, but this requires a long processing time and is inefficient. Japanese Patent Application Publication No.6-188472 makes no disclosure regarding a concrete method for forming the recess and projecting shapes, and the above-described methods respectively involve the problems stated above. Although other methods might be envisaged, such as calcination followed by sandblasting, or calcination performed after forming the recess and projecting shapes, these methods require complicated post-processing steps and have poor accuracy. Moreover, performing calcination after forming the shapes will disrupt the dimensional accuracy.